The invention relates to detection of a process endpoint during a substrate fabrication process.
In substrate fabrication processes, semiconductor, dielectric, and conductor materials, including for example materials such as polysilicon, silicon dioxide, aluminum and tungsten silicide, are formed on a substrate by chemical vapor deposition (CVD), physical vapor deposition, oxidation and nitridation processes. For example, in CVD processes, a reactive gas may be used to deposit material on the substrate, and in PVD processes, a target is sputtered to deposit material on the substrate. In oxidation and nitridation processes, an oxide or nitride material, such as silicon dioxide or silicon nitride, respectively, is formed on the substrate by exposing the substrate to a suitable gaseous environment. In subsequent etching processes, a mask of photoresist or hard mask material is formed on the substrate by conventional lithographic methods, and the exposed portions of the substrate are etched by a gas to form patterns of gates, vias, contact holes or interconnect lines. Especially in the etching processes, it is often desirable to change or stop processing of the substrate at a predetermined stage of the process. For example, when etching polysilicon material deposited over features of a silicon nitride mask layer, it is desirable to stop etching when the silicon nitride mask layer is reached and thereafter partially etching polysilicon plugs exposed between the silicon nitride layer. As another example, in the etching of gate structures, it is desirable to stop etching of overlying polysilicon as soon as the underlying gate oxide is reached, especially when the gate oxide is a thin layer.
In plasma emission analysis, an emission spectrum of a plasma in the chamber is analyzed to monitor the etching process as for example taught in U.S. Pat. Nos. 4,328,068 and 5,362,256, both of which are incorporated herein by reference. The plasma emission spectrum depends upon the energized plasma species which are dependent upon the composition of the material being etched. When the composition of the material changes, for example, when a layer has completed etching and an underlayer is exposed, the spectral change that occurs in the plasma is used to detect completion of etching of the overlying material. In general, plasma emission methods monitor a predetermined wavelength in the plasma spectral emission and correlate variations in intensity of the wavelength with an endpoint of the process. However, such spectral changes occur only after a large portion of a new material is exposed on the substrate. Thus plasma emission analysis tends to provide information relating to an average state of processing across the surface of the substrate. This may lead to some regions being over-etched while others are under-etched.
Ellipsometry and interferometry are also be used to monitor the etching process. In ellipsometry, a polarized light beam reflected off the substrate being etched is analyzed to determine a phase shift and change in magnitude, as for example disclosed in U.S. Pat. Nos. 3,874,797 and 3,824,017, both of which are incorporated herein by reference. In interferometry, a light beam reflected off the substrate is monitored and an etching depth is determined by counting maxima and minima in the amplitude of the reflected beam or from cessation of the signal, as for example disclosed in U.S. Pat. No. 4,618,262 to Maydan et al, which is also incorporated herein by reference. The constructive and destructive interference occurs because the light beam is partially reflected off the substrate surface and partially reflected off underlying interfaces. If the original thickness of the layer is known, a remaining thickness may be estimated by counting the maxima/minima peaks during etching. While these methods may be used to estimate the amount of remaining material, it is difficult to precisely determine the end of etching of the material, especially when the original thickness of the material varies slightly from one substrate to another or across the surface of the substrate itself. Also, the area on the substrate from which initial thickness measurements are obtained is often not the same area as that from which the reflected beam is monitored, which may give rises to erroneous measurements.
Thus, it is desirable to precisely detect an endpoint of processing of a material on a substrate, especially to detect an endpoint of etching a layer on a substrate to expose an underlayer. It is further desirable for the endpoint detection method and apparatus to be relatively insensitive to changes in thickness of the layer across the substrate or from one substrate to another.
Embodiments of the present invention satisfy these needs, in principle, by detecting an endpoint of a process performed on a substrate with accuracy and repeatability. In one aspect, the present invention comprises a substrate processing apparatus comprising a process chamber capable of processing a first material on the substrate. A radiation source is capable of emitting radiation that is reflected from the substrate during processing. A radiation detector is provided to detect the reflected radiation and generate a signal trace. A controller is adapted to receive the signal trace and evaluate an endpoint of processing the first material from a change in the signal trace that is distinctive of an exposure of a second material having a different reflectivity coefficient than the first material.
In one version, the apparatus comprises a computer having a memory capable of operating a computer-readable program embodied on a computer-readable medium, the computer readable program including program code to receive the signal trace and detect the change in the signal trace.
In another aspect, the present invention relates to a method of processing a substrate, in which, the substrate is placed in a process zone, and process conditions are set in the process zone to process a first material on the substrate. Radiation reflected from the substrate during processing is detected and an endpoint of processing the first material is determined from a change in intensity of reflected radiation that is distinctive of exposure of a second material having a different reflectivity coefficient than the first material.
In another aspect, the present invention relates to a substrate processing apparatus comprising a process chamber capable of sustaining a plasma to process a first material on the substrate. A first radiation detector detects a radiation emission from the plasma and generates a first signal, and a second radiation detector detects a reflected radiation from the substrate and generates a second signal. A controller is adapted to receive the first and second signals and determine an endpoint of processing of the first material on the substrate.
In one version, the apparatus comprises a computer having a memory capable of operating a computer-readable program embodied on a computer-readable medium, the computer readable program including program code to receive the first and second signals and determine an endpoint of processing the first material on the substrate.
In another aspect, the present invention relates to a method of processing a substrate, in which, the substrate is placed in a process zone, and a plasma of process gas is formed in the process zone to process a first material on the substrate. Radiation emitted by the plasma and radiation reflected from the substrate are detected. An endpoint of processing the first material is determined from a change in the radiation emitted by the plasma and a change in the radiation reflected from the substrate.